1. Field of the Invention
The present invention relates to an optical scanning device which can be used, for example, in a laser printer or similar device.
2. Description of Related Art
In a laser printer in which a photosensitive medium, such as a photosensitive drum, is scanned with scanning beams which are moved in a main scanning direction and which are converged onto the photosensitive medium to write data to be printed thereon, the timing of the data writing, at which the recording of data to be printed onto the photosensitive medium begins, is determined in accordance with the time at which the beams are detected at a predetermined position on the upstream side of scanning beams in the main scanning direction. To this end, a beam detector is provided, in the laser printer mentioned above, to detect the scanning beams at the commencement of the scanning.
The beam detector is preferably located at the position where the scanning beams are converged. However, if the beam detector is disposed at the beam convergent point on the upstream side of the scanner, the optical scanning device becomes large, and the optical detector interferes with the photosensitive medium. To prevent this, one or a plurality of reflecting mirrors and lenses are provided to reflect the scanning beams toward the beam detector, which is located at a position in which no interference with the photosensitive medium occurs, on the upstream sides of the scanning beams in the main scanning direction.
FIG. 7 shows a known optical scanning device, including a collimator 3 which collimates the laser beams emitted from a laser diode LD (not shown), a converging lens 4, a polygonal mirror 5, an f.theta. lens 6, a BD mirror (horizontal synchronization mirror) 8, a lens holder 10 having a converging lens 9, and a beam detector 11, in a housing 2 of an optical scanning device 30.
In the optical scanning device 30, the beam "A" emitted from the laser diode through the collimator 3 is deflected by the polygonal mirror 5 in the main scanning direction M, so that the scanning beam A1 thus deflected can be converged onto the photosensitive drum (not shown) by the f.theta. lens 6. The timing of the writing at which the data to be printed is written onto the photosensitive drum is determined in accordance with the time at which the beam A2, reflected by the BD mirror 8 and converged by the converging lens 9 at the commencement of the scanning, is detected by a light receiving element 12 of the beam detector 11.
In the known scanning apparatus 30 mentioned above, since the scanning beam A2, at the commencement of scanning, is made incident upon the beam detector 11 through the BD mirror 8 and the converging lens 9, the BD mirror 8 must be mounted to the housing 2 with an extremely high precision.
Namely, if the BD mirror 8 is mounted to the housing 2 at a position slightly deviated from a predetermined position, the scanning beam A2, reflected by the BD mirror 8, is considerably deviated from a predetermined light path, the result being that the detection timing of the scanning beams A2 detected by the light receiving element 12 is deviated from a correct timing, thus leading to an incorrect timing of the writing of the printing data onto the photosensitive drum (not shown).
To prevent this, an adjusting mechanism (not shown) is provided on the BD mirror 8 of the optical scanner 30 to adjust the mounting position thereof to the housing 2. The BD mirror 8 is mounted to the housing 2 while adjusting the mounting position thereof by the adjusting mechanism so as to be able to correct the path of the scanning beam, within a predetermined tolerance, towards the light receiving element 12 of the beam detector 11. However, this adjusting operation, provided on the BD mirror 8, is troublesome. Moreover, the adjusting mechanism increases the manufacturing cost.